Comment 3 for bug 1602614

Change abandoned by venkata anil (<email address hidden>) on branch: master
Review: https://review.openstack.org/323314
Reason: Prefering patch 255237 over this
1) Backporting alembic migration may not be allowed
2) To avoid special handling for TOR drivers

note: We may visit these patches(340031, 324302, 323314) later to solve 1488015.